Various systems and devices utilizing fiber optics to convey optical energy, such as an image, are well known in the art. In addition, the use of fiber optical elements near focal planes is also well known in the art. Indeed, fiber optics technology is utilized in a wide variety of applications for transmitting voice, video, and data signals. Fiber optic cables have significant advantages over electrical voice, video and data signal carriers, one of which is their capacity for increased data transfer.
A typical fiber optic cable includes a silica core (glass optical fiber element), a silica cladding, and a protective coating. The glass optical fibers of fiber optic cables have very small diameters, which are susceptible to external influences such as mechanical stress and environmental conditions. The index of refraction of the core is higher than the index of refraction of the cladding to promote internal reflection of light propagating down the core.
Recently, fiber optic elements have been utilized with imaging sensors or imaging arrays to create an imaging system. These systems are typically called fiber face plates and are associated with image intensifiers used in the visible and near-infrared portion of the electromagnetic spectrum.
When an image is formed on a detector array, the image is pixilated. The energy in each pixel is represented electronically in the form of digital bits. Unless some sort of spectral filter is used, this electronic image will include all wavelengths of light to which the detector is sensitive. This monochromatic or single spectral band type of sensor would record overall irradiance at the pixel but would result in a loss of color information.
There are also several types of color imaging systems. A typical imaging sensor uses red, green and blue as primary colors. The system may include red, green and blue transmissive filters or beamsplitters. A color image may be built up in a time sequential fashion by positioning the filters in front of a single detector array in a time sequenced fashion. Alternatively, the color image may be created by splitting the incoming beam of light into red, green, and blue components using the spectral filters and then imaging the beam on to three separate detector arrays; one each for the red, green, and blue colors. Another method of creating a color image is to use spectral filters directly on or close to the detector array distributed according to some predetermined color pattern. One such commonly used pattern is the Bayer pattern.
Prior to the present invention, several electronics instruments for remotely sensing light have been built using the traditional filter deposited on a substrate, including the ALI, ASTER, MISR, MODIS, and SeaWiFS. The disadvantage of the traditional filter substrate approach is that light can couple into adjacent spectral bands. This has been partially solved by placing an opaque layer between the different substrates and filters but this process is still dependent on cutting small pieces that are pre-coated or subsequently coating them. The small pieces must then be glued together to form the final filter. FIG. 11 shows the crosstalk problems and how some of them have been partially addressed in the past.